Automatically controlled floatation apparatus and method



H. H. PICK ET AL 3,471,010

AUTOMATICALLY CONTROLLED FLOATATION APPARATUS AND METHOD Oct. 7, 1969Filed Nov. 21, 1966 INVENTORS:

L IV T 5 m w i S m WM 8 C R N 0 R T WC M T P A (A .w M H 8 S NWA AA w HRR K C W United States Patent 3,471,010 AUTOMATICALLY CONTROLLEDFLOATATION APPARATUS AND METHOD Hans H. Pick and Ralph W. Crosser, Jr.,Salt Lake City,

Utah, assignors to Kennecott Copper Corporation, New

York, N.Y., a corporation of New York Filed Nov. 21, 1966, Ser. No.600,684 Int. Cl. B03b 13/04 US. Cl. 209-1 9 Claims ABSTRACT OF THEDISCLOSURE with such a flotation cell, an electrical capacitance probearranged above the froth overflow lip of the cell.

The invention This invention relates to .method and apparatus forcarrying out flotation procedures in the separation of particles ofvarious materials, such as minerals of different types, by processes offroth flotation, wherein an aqueous pulp of the material particles to beseparated is subjected to aeration in a flotation machine to produce afroth overflow carrying certain of the particles and a tailingsdischarge carrying the other particles.

Flotation machines are normally made up of a series of individual cells,with the feed material flowing from cell to cell. Froth rises in andoverflows from each cell to a launder for segregated discharge, whilethe ailings from one cell flow into the next cell in line as the feedfor that cell. It is important that the liquid level in each cell becontrolled to maintain optimum conditions for separation of the materialparticles concerned. This is normally accomplished by means of gatesbetween the individual cells regulating tailings discharge from one cellto a succeeding cell or from the last cell in line, the gates beingindividually manipulated toetfect the desired liquid level control. I

In some instances, instead of gates other types of tailings dischargedevices are employed, for example, plug valves. Also, in some instances,flotation machines are not divided into cells, in which event a singletailing discharge controls the liquid level along the entire length ofthe machine.

Liquid levels in flotation machines have been automatically controlledheretofore by devices that sense the varying hydrostatic heads of theliquid pulp in the respective cells and that effect opening or closingof respective gates by feeding signals into motorized power systems foroperating such gates.

In accordance with the present invention, however, the quantity of frothoverflowing from a flotation cell is sensed continuously, and thetailings discharge gate for such cell is raised or lowered to a greateror lesser extent, or whatever other type of tailings discharge devicemay be used in the particular instance is appropriately manipulated, inaccordance with variations in such quantity.

. Continuous sensing of the quantity of froth overflow can beeffectively accomplished in various ways, which represent specificaspects of the present invention.

Thus, the froth passing over a small portion of the total length of theoverflow lip of a flotation cell may be continuously conducted into asensing device, comprismg a relatively small sampling vessel havinggravity discharge opening such that a body of material, reflectingfluctuations in inflow to such vessel, is maintained in the vessel. Astandard type of air bubbler tube detects changes in hydrostatic head ofsuch body of material, which consists of froth repulped in the vessel bya continuous spray of water. By keeping the supply of spray Waterconsistent, the level of the body of repulped froth fluctuates inaccordance with fluctuations in the level of froth overflow from theflotation cell, and such changes in level are continuously sensed by theair bubbler tube and used to control a suitable motivating device, suchas an electric motor, for the tailings discharge device by means ofsuitable circuitry which may be of well known type.

Again, a sensing device in the form of a plate-type capacitanceproximity probe may be employed, together with standard electricalcontrol circuitry for the actuating motor. The detector plate of theprobe is mounted above and in spaced relationship with the frothoverflow lip of the flotation cell and extends lengthwise with such lip.It senses variations in froth overflow level by reason of correspondingchanges in spacing of the surface of the overflowing froth from thedetector plate.

Other suitable types of sensing arrangements may, of course, be used inplace of those specifically indicated above, but such specificallyindicated arrangements are presently believed to be the best modes ofcarrying out the invention and are, consequently, illustrated anddescribed in detail.

In the drawing:

FIG. 1 is a schematic perspective view of a typical single cellflotation machine, with which is combined a sampling vessel andair-bubbler tube 'type of froth overflow level sensing arrangement;

FIG. 2, a schematic view showing the sampling vessel and a fragment ofthe froth overflow lip of the flotation machine in vertical centralsection, with parts of a standard wiring diagram connecting sensingcomponents of such sampling vessel with actuating mechanism for raisingand lowering the tailings discharge gate of the flotation machine, whichmechanism and gate are shown inelevation.

FIG. 3, a fragmentary vertical section taken on the line 33 of FIG. 2and drawn to a larger scale;

i FIG. 4, a similar view taken on the line 4--4 of FIG.

; and

FIG. 5, a view similar to that of FIG. 2 but showing a different form ofthe apparatus of the invention, wherein a plate-type capacitance probeis utilized to sense changes in the level of froth overflowing thefroth-overflow lip of the machine.

Referring to the drawing:

In the embodiment of FIGS. l-4, the single cell flotation machineillustrated schematically is typical of standard installations. Itcomprises an elongate tank 10' into which flotation pulp is fed througha usual feed box 11.

As is common, a plurality of impellers (not shown) are mounted forrotation at the lower ends of respective ir'npeller shafts 12 powered byrespective electric motors 13. Mineral-laden froth rises to the surfaceof the body of pulp in tank 10 and discharges into lounder 14 over anelongate froth overflow lip 15. As usual, the tailings pass intotailings-box 16 through submerged outlet openings (not shown) anddischarge over tailings gate 17, either into a next succeeding cell (notshown) at a lower level,

for repeated flotation treatment, or directly to Waste if minedcapacity, which in this instance, is a valved, gravity discharge Opening18a, is fed with a continuously flowing sample of the over-flowing frothby means of a sampling launder 19. The vessel 18 is advantageously ofinverted frusto-conical formation, converging to a bottom opening, 18a,and such opening is advantageously valved by means of a plug 20 at theend of a stem 21 that is movable upwardly and downwardly in a supportingarm 22. Thus, the size of discharge opening 18a can be predetermined asdesired for any given operation of the machine, and a body of materialcan be established and continuously maintained in the vessel 18 toreflect variations in quantity of froth inflow from time to time.

Provision is made for re-pulping the froth samples as they pass throughsampling vessel 18. In the illustrated instance, a spray ring 23 ispositioned over the interior of the sampling vessel, being supplied withwater through pipe 24 under the control of a valve, as indicated.

In order to automatically control the raising and lowering of tailingsgate 17 in accordance with fluctuating froth overflow levels from theflotation tank 10, a bubble tube 25, supplied with low-pressure air fromvalved air supply lines 26, is positioned to dip below the normal liquidlevel in sampling vessel 18 and to detect changes in hydrostatic head ofthe body of re-pulped froth maintained in such vessel.

Pressure differentials are used in well known manner to control anelectrical switch 27 of standard type, which regulates the supply ofelectricity through circuit 28 to a reversible motor 29 that is adaptedto raise or lower tailings gate 17, depending upon the direction ofoperation of such motor on any given activation thereof. The particulardirection of operation, either forward or reverse, will, of course,depend upon whether the hydrostatic pressure in vessel 18 is eitherlowered or raised to trip switch 27.

As here illustrated, the mechanism by which motor 29 either raises orlowers tailings gate 17 comprises a lever 30, fulcrumed at one end by apivot mounting 31 positioned on top frame member 32a of tailings gateframe 32, and an eccentric drive connecting the output shaft 29a of themotor to the free end of the lever.

The usual handwheel mechanism for normally raising or lowering the gateis modified by rotatably mounting the hub, 33a, of such handwheel, 33,in a bearing mount 34 that is swiveled by stub pins 34a in lever 30. Asplit ring 35, FIG. 3, fits into a circumferential groove 36 ofhandwheel hub 33a and holds the handwheel in place as it is turned toscrew the threaded stern 17a of gate 17 either upwardly or downwardly,such split ring being bolted to bearing mount 34, and the swivelmounting of pins 34a being sufiiciently loose to accommodate the smallamount of arcuate movement occurring as lever 30 is raised and lowered.

As illustrated, the eccentric drive between motor 29 and lever 30comprises a disk 37, FIG. 4, secured to motor shaft 29a and providedwith a crank pin 37a, which is connected to the free end of lever 30 bymeans of a connecting rod 38. v

A different type of sensing arrangement is shown in FIG. 5, where anelectrical capacitance proximity probe 40 is employed to directly detectchanges in level of froth 41 overflowing lip 15. The changes in frothlevel produce corresponding changes incapacitance by reason of increaseor decrease of the dielectric space or air gap 42 between an elongatedetector plate 40!: and the superficial surface of the overflowing froth41. Such detector plate should, for best results, extend alongsubstantiallythe entire length of a portion of overflow lip 15 that iss11b, ject to the action of an impeller unit represented by a shaft 12and motor 13. In the particular cell illustrated, this is approximatelyone-quarter the length of lip 15, and the detector plate advantageouslyextends symmetrically at opposite sides of such shaft 12 and motor 13and parallel with the superficial surface of the overflowing froth,

as indicated in FIG, 5, to provide a control for the en: tire cell. Itis obvious that the mineral content in the froth will play a part in theelectrical output of the sensing device as well as changes in the frothlevels.

The detector plate 40a should extend over a representative area of theoverflowing stream of froth. The usual downwardly-sloping apron 15a ofthe overflow lip of the flotation cell provides an effective detectionsurface for the overflowing froth. It is preferable that the width ofdetector plate 40a be commensurate therewith, as illustrated. Both thecapacitance probe 40 and the electrical control circuit therefor (merelyindicated at 43), may be of standard type, such as provided by thecommercial level measuring and indicating system manufactured and soldby Aeronautical and Instrument Division, Robertshaw Controls Company,Anaheim, Calif, as detailed in its Bulletin 30 under the tradedesignation Level-Tel Model 305, which advantageously includes a visualdisplay unit 44 to indicate how the system is operatingand to housevarious circuit components, which need not be detailed here.

We claim:

1. Automatically controlled flotation apparatus, including incombination:

a flotation cell, comprising a tank having an elongate froth overflowlip, pulp feed, and variable tailings discharge means;

power means for varying said tailings discharge means;

means for continuously sensing variations in the quantity of frothoverflowing said lip of the flotation cell; and

control circuitry between the sensing means and the power means fortranslating sensed changes in froth quantity into related changes inpower applied to said power means, whereby the tailings discharge willbe varied in accordance with variations in froth quantity. i

p 2. Apparatus as recited in claim 1, wherein the means for sensingvariations in the quantity of froth overflowing the lip of the flotationcell comprises:

a froth sampling vessel having continuously operating discharge means ofpredetermined capacity for material flowing into said vessel;

a sampling launder leading from a localized area along said lip of theflotation cell into said sampling vessel;

means for continuously mixing a re-pulping liquid with samples of frothin said sampling vessel;

an air-bubbler tube in said sampling vessel, with its discharge enddisposed below the normal level of'repulped froth therein and below thelowest point of variation of said level;

means for supplying air under pressure to said bubbler tube; and

wherein the control circuitry between the sensing means and the powermeans includes electrical switch means responsive to changes in pressureof the air being supplied said bubbler tube.

3. Apparatus as recited in claim 2, wherein the sampling vessel is ofinverted frusto-conical formation, with the discharge means being avalved opening at the downwardly-directed, convergent bottom of saidvessel.

4. Apparatus as recited in claim 2 wherein the means for continuouslymixing a re-pulping liquidwith samples of froth in the sampling vesselcomprises a spray nozzledirected inwardly of said vessel, and meansfor'supplying water under pressure to said spray nozzle.

5. Apparatus as recited in claim 1, wherein the means for sensingvariations in the quantity of froth overflowing the lip of the flotationcell comprisesz' an electrical capacitance probe having an elongatedetector plate spaced above said lip of the flotation cell and extendingalong the length thereof.

6. Apparatus as recited in claim 5,'wherein'the detector plate has awidth substantially equal to the width of the apron portion of theoverflow lip.

7. A method of automatically controlling the operation of a flotationmachine, comprising continuously sensing the quantity of froth overflowduring operation of the machine to produce signals indicative ofvariations in said quantity; and utilizing said signals to control thequantity of tailings discharged from the machine so as to keep the pulplevel in the machine substantially constant. 8. A method as' recited inclaim 7, wherein the quantity of froth overflow is sensed bycontinuously repulpin'g a portion of the normal froth overflow from themachine, and by sensing variations in pressure of air discharged belowthe fluctuating surface of the repulped portion of said froth overflow.

of froth overflow is sensed on the basis of variations in electricalcapacitance brought about by variations in froth discharge across thefroth overflow lip of the machine.

References Cited UNITED STATES PATENTS 1,708,075 4/ 1929 Allen.

2,931,502 4/1960 Schoeld 209-164 3,255,882 6/1966 McCarty -.1 209-13,282,217 11/1966 Slover l37392 X HARRY B. THORNTON, Primary Examiner R.HALPER, Assistant Examiner US. Cl. X.R.

